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Fluid Friction.

The head H is determined by a stake placed in still water
above the notch.    (Seep. 1201.)

Fluid Friction.—The general laws, p. 557, state that
Fnoc #2, and is independent of pressure, but depends directly on
the wetted surface. Measuring the surface area A in square feet,

Fn   =

at moderate speeds, where p = "004 for clean varnished surfaces,
and -009 for a medium sand-paper texture (Froude).

Friction in Pipes is principally due to surface or skin
friction, viscous resistance being extremely slight. Assuming
G = 2g approximately, and placing these values so as to cancel,

Total Fn =

Supposing, now, a piece of water of length L and diameter D
of the pipe, is being pushed through the latter at velocity v:

Fn per sq.ft. of I
sectional area  J      r

As

~, we divide by G, and obtain

Head lost in friction

(SeeAppendixIV.,
/• 965.)